Dioxygen reduction to water provides the major energetic driving force for living cells and with reversal, light driven oxidation of water, requires enzymes to catalyze cyclic reaction series via highly reactive chemical intermediates. The primary structure and reactions of oxygen reductases, currently with P450 is almost half completed and our intensive continuing effort will soon be aided by crystallographic data. Sulfhydryl groups critical to the monoxygenase catalysis are indicated by protein modification and resonance spectral measurements. Six cysteinyl peptides containing seven cysteines and a total of about 100 residues have been sequenced. Stable isotope substitution by growth of 57/54 Fe, 34/32S, 15/14N, 13/12C, and 2/1H and resolution of the heme and protein moieties followed by reciprocal reconstitution has provided amorphous and crystalline P450 for resonance probe characterization of the heme pocket ligands in the stable reaction states of dioxygen reductive cleavage with hydrocarbon oxygenation. Protein dimensions and configuration are initiated via low angle and x-ray analysis and additional crystalline derivatives are in preparation for characterization of the redoxin P450 iron-iron redox couple.